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Construction of the World Trade Center

The construction of the first World Trade Center complex in New York City was conceived as an urban renewal project to help revitalize Lower Manhattan spearheaded by David Rockefeller. The project was developed by the Port Authority of New York and New Jersey. The idea for the World Trade Center arose after World War II as a way to supplement existing avenues of international commerce in the United States.

This article is about the construction of the original World Trade Center. For the construction of the new World Trade Center after the September 11 attacks, see World Trade Center (2001–present) § Rebuilding.

World Trade Center

Lower Manhattan, New York City

August 5, 1966 (August 5, 1966)[2]

  • 1 WTC: August 6, 1968
  • 2 WTC: January 1969
  • 3 WTC: March 1979
  • 4 WTC: 1974
  • 5 WTC: 1970
  • 6 WTC: 1969
  • 7 WTC: October 2, 1984

  • 1 WTC: December 23, 1970
  • 2 WTC: July 19, 1971

  • 1 WTC: 1972
  • 2 WTC: April 4, 1973[1]
  • 3 WTC: April 1, 1981
  • 4 WTC: 1975
  • 5 WTC: 1972
  • 6 WTC: 1973
  • 7 WTC: March 1987

  • 1 WTC: December 15, 1970
  • 2 WTC: January 1972
  • 3 WTC: July 1, 1981[3]
  • 4 WTC: January 1977
  • 5 WTC: March 1972
  • 6 WTC: January 1974
  • 7 WTC: May 1987

April 4, 1973 (April 4, 1973)

1 WTC: 1,728 feet (526.7 m)

1 WTC: 1,728 feet (526.7 m)

  • 1 WTC: 1,368 feet (417.0 m)
  • 2 WTC: 1,362 feet (415.1 m)
  • 3 WTC: 250 feet (76.2 m)
  • 4 and 5 WTC: 120 feet (36.6 m)
  • 6 WTC: 110 feet (33.5 m)
  • 7 WTC: 610 feet (185.9 m)

  • 1 WTC: 1,355 feet (413 m)
  • 2 WTC: 1,348 ft (411 m)

  • 1 and 2 WTC: 110 floors
  • 3 WTC: 22 floors
  • 4 and 5 WTC: 9 floors
  • 6 WTC: 8 floors
  • 7 WTC: 47 floors

  • 1 and 2 WTC: 4,300,000 sq ft (400,000 m2) each
  • 4, 5, and 6 WTC: 500,000 sq ft (50,000 m2) each
  • 7 WTC: 1,868,000 sq ft (170,000 m2)

1 and 2 WTC: 99 each

Port Authority of New York and New Jersey

Worthington, Skilling, Helle & Jackson,[4] Leslie E. Robertson Associates

Tishman Realty & Construction Company

The World Trade Center was originally planned to be built on the east side of Lower Manhattan, but the New Jersey and New York state governments, which oversee the Port Authority, could not agree on this location. After extensive negotiations, the New Jersey and New York state governments agreed to support the World Trade Center project, which was built at the site of Radio Row in the Lower West Side of Manhattan, New York City. To make the agreement acceptable to New Jersey, the Port Authority agreed to take over the bankrupt Hudson & Manhattan Railroad, which brought commuters from New Jersey to the Lower Manhattan site and, upon the Port Authority's takeover of the railroad, was renamed PATH.


The Port Authority hired architect Minoru Yamasaki, who came up with the specific idea for twin towers. The towers were designed as framed tube structures, which provided tenants with open floor plans, uninterrupted by columns or walls. This was accomplished using numerous closely spaced perimeter columns to provide much of the strength to the structure, along with gravity load shared with the core columns. The elevator system, which made use of sky lobbies and a system of express and local elevators, allowed substantial floor space to be freed up for use as office space by making the structural core smaller. The design and construction of the World Trade Center, most centrally its twin towers, involved many other innovative techniques, such as the slurry wall for digging the foundation, and wind tunnel experiments.


Construction of the World Trade Center's North Tower began in August 1968, and the South Tower in 1969. Extensive use of prefabricated components helped to speed up the construction process. The first tenants moved into the North Tower in December 1970 and into the South Tower in January 1972. Four other low-level buildings were constructed as part of the World Trade Center in the early 1970s, and the complex was mostly complete by 1973. A seventh building, 7 World Trade Center, was opened in 1987.

Planning[edit]

Context[edit]

In 1942, Austin J. Tobin became the Executive Director of the Port Authority, beginning a 30-year career during which he oversaw the planning and development of the World Trade Center.[7] The concept of establishing a "world trade center" was conceived during the post–World War II period, when the United States thrived economically and international trade was increasing.[8] At the time, economic growth was concentrated in Midtown Manhattan, in part stimulated by Rockefeller Center, which had been developed in the 1930s.[9]


In 1946, a year after the war formally ended, the New York State Legislature passed a bill that called for a "world trade center" to be established. This trade center would increase New York City's role in transatlantic trade.[10][11] The World Trade Corporation was founded, and a board was appointed by New York Governor Thomas E. Dewey to develop plans for the project.[10][12] The concept was inspired by the Leipzig Trade Fair, which had been considered "the marketplace of all Europe" before being destroyed during World War II.[13][14] Less than four months after the board was named, plans for a "world trade center" were put on hold.[12] By then, architect John Eberson and his son Drew had devised a plan that included 21 buildings over a ten-block area, at an estimated cost of $150 million.[15][11] Projections determined that such a complex would not be profitable due to a lack of demand. One estimated that the World Trade Center project would only be successful if at least 4,800 of the United States' largest 6,000 companies were involved.[11] In 1949, the World Trade Corporation was dissolved by the New York State Legislature.[16]

Typical Twin Tower floor framing

Typical Twin Tower floor framing

96th floor core of WTC 1. This floor structure configuration is typical.

96th floor core of WTC 1. This floor structure configuration is typical.

Schematic of composite floor truss system

Schematic of composite floor truss system

Modifications[edit]

Over time, numerous structural modifications were made to suit the needs of tenants in the Twin Towers. Modifications were made in accordance with the Port Authority's Tenant Alteration Review Manual and were reviewed by the Port Authority to ensure the changes did not compromise structural integrity of the buildings. In many instances, openings were cut in the floors to accommodate new stairways to connect tenant floors. Some steel beams in the core were reinforced and strengthened to accommodate heavy live loads, such as large amounts of heavy files that tenants had on their floors.[175]


Repairs to structural elements on the lower levels of 1 WTC were made following the 1993 bombing. The greatest damage occurred on levels B1 and B2, with significant structural damage also on level B3.[176] Primary structural columns were not damaged, but secondary steel members experienced some damage.[177] Floors that were blown out needed to be repaired to restore the structural support they provided to columns.[178] The slurry wall was in peril following the bombing and loss of the floor slabs which provided lateral support to counteract pressure from Hudson River water on the other side.[179]


The refrigeration plant on sublevel B5, which provided air conditioning to the entire World Trade Center complex, was heavily damaged and replaced with a temporary system for the summer of 1993.[179] The fire alarm system for the entire complex needed to be replaced, after critical wiring and signaling in the original system was destroyed in the 1993 bombing. Installation of the new system took years to complete; replacement of some components was still underway in September 2001, at the time of the attacks that ultimately destroyed the complex.[180]

Construction in 1969

Construction in 1969

Construction on January 11, 1971

Construction on January 11, 1971

Construction on January 12, 1971

Construction on January 12, 1971

Cudahy, Brian J. (2002), (2nd ed.), New York: Fordham University Press, ISBN 978-0-82890-257-1, OCLC 911046235

Rails Under the Mighty Hudson

Gillespie, Angus K. (1999). . Rutgers University Press. ISBN 978-0-8135-2742-0.

Twin Towers: The Life of New York City's World Trade Center

Glanz, James & Lipton, Eric (2003). City in the Sky. Times Books.  978-0-8050-7691-2.

ISBN

Goldberger, Paul (2004). . Random House Publishing Group. ISBN 978-1-58836-422-7.

Up from Zero: Politics, Architecture, and the Rebuilding of New York

Lew, Hai S.; Bukowski, Richard W.; Carino, Nicholas J. (September 2005). (Report). Federal Building and Fire Safety Investigation of the World Trade Center Disaster. National Institute of Standards and Technology (NIST).

Design, Construction, and Maintenance of Structural and Life Safety Systems (NIST NCSTAR 1–1)

Evans, David D.; Richard D. Peacock, Erica D. Kuligowski; W. Stuart Dols; William L. Grosshandler (September 2005). (Report). National Institute of Standards and Technology.

Active Fire Protection Systems (NCSTAR 1–4)

National Construction Safety Team (September 2005). (Report). Structural Fire Response and Probable Collapse Sequence of the World Trade Center Towers. National Institute of Standards and Technology (NIST).

Federal Building and Fire Safety Investigation of the World Trade Center Disaster (NCSTAR 1–6)

Sivaraj Shyam-Sunder; Richard G. Gann; William L. Grosshandler; Hai S. Lew; Richard W. Bukowski; Fahim Sadek; Frank W. Gayle; John L. Gross; Therese P. McAllister; Jason D. Averill; James R. Lawson; Harold E. Nelson; Stephen A. Cauffman (September 2005). (PDF) (Report). Federal Building and Fire Safety Investigation of the World Trade Center Disaster. National Institute of Standards and Technology (NIST).

Final Report of the National Construction Safety Team on the Collapses of the World Trade Center Tower (NIST NCSTAR 1)

– Building the World Trade Center, an 18-minute film, with construction footage, produced by the Port Authority in 1983

New York: A Documentary Film – The Center of the World

– Skyscraper Museum

World Trade Center

40°42′42″N 74°00′49″W / 40.71167°N 74.01361°W / 40.71167; -74.01361